Acid pickling compositions and method of pickling



Patented Oct. 19, 1954 ACID PICKLINO COMPOSITIONS AND METHOD OF PICKLING Allan E. Chester, Highland Park, Ill., and Joseph T. Irwin, Lakewood, Ohio; said Chester assignor to Poor &- Company, Chicago, Ill., 2. corporation of Delaware No Drawing. Application October 18. 1951, Serial No. 251,982

. 14 Claims.

This invention relates to the acid pickling of metals, more particularly the acid picklin of steel, and to new and useful pickling'compositions. v

One of the objects of the invention is to provide a new and improved method of pickling ferrous metals by a process in which the rate of pickling is greatly accelerated.

Another object is to provide new and useful addition agents for sulfuric acid and hydrochloric acid pickling solutions which are effective in unifying the electrostatic charge over ferrous metal surfaces and removing hydrogen films from cathodic areas, thus creating a uniform microetch without excessive acid attack on anodic areas or crystalboundaries.

Another object of the invention is to provide a new and improved method of acid pickling ferrous metals which functions to prevent the oxidation of aqueous solutions of iron salts remaining on the surface of ferrous metals which have been immersed in sulfuric acid or hydrochloric acid pickling solutions.

Another object of the invention is to provide new and useful pickling compositions which can be added to acid pickling baths in order to produce new and improved results. Other objects will appear hereinafter.

In accordance with this invention these objects are accomplished by providing a pickling bath containing a compound capable of liberating c01- loidal sulfur, preferably sodium thiosulfate, and a water soluble ionizable thiocyanate, preferably sodium thiocyanate.

The employment of a substance such as sodium thiosulfate which liberates'colloidal sulfur in the pickling solution is not claimed herein per se but is the subject of another application of one-of the joint inventors, United States application Serial No. 694,424, filed August 31, 1946, now Patent No. 2,636,009. It will be understood that other substances capable of liberating colloidal sulfur as, for example, sodium polysulfide may be employed in the practice of the invention.

The thiocyanate makes it possible to-obtaina more finely grained etch. It will be understood that other water soluble ionizable thiocyanates such as, for example, potassium and ammonium thiocyanates may be employed to replace apart or all of the sodium thiocyanate.

The invention will be illustrated but isnot limited by the following examples in which-the quantities are stated in parts by weight unless otherwise indicated.

3 Example I A composition suitable for use as an addition agent to an acid picklin bath was prepared by mixing together the following ingredients:

644 pounds sodium thiocyanate 161 pounds sodium thiosulfate 1936 pounds dextrose 4 pounds caustic soda.

46 pounds Aerosol OS (isopropylnaphthalene sodium salt) and enough water to make 480 gallons of solution.

A hydrochloric acid pickling bath was prepared containing 10'to 15% HCl. The composition described in Example I was added to this bath in proportions of 4 to 8 cc. for each gallon of pickling solution.- Thereafter 1 to 2 gallons of the composition of Example I were added for each thousand gallons of hydrochloric acid added to the solution as long as use of the pickling bath was continued. Cold rolled carbon steel sheets were pickled in this bath with excellent results.

Example III The pickling procedure was the same as that described in Example II except that the acid pickling bath contained 6 to 20% sulfuric acid. One to two gallons'of the composition of Example I were added for each thousand pounds of sulfuric acid added to the solutionas long as it was used. 7

The time required for the pickling procedure will vary depending upon a number of factors, for example, whether a continuous or batch type pickling operation is used. However, by employing the addition agent of the present invention the time period can be reduced to about two thirds of the time normally required in acid pickling operations using an ordinary inhibited pickling acid. Thus inpickling low carbon SAE 1020 rods, if 30 minutes were required in ordinary pickling,* the desired result can be obtained with a pickling bath containing a composition as herein described inapproximately 20 minutes. 'Actual plant practice will vary"considerably depending ing agent.

3 also upon the type of material which is being pickled.

In the foregoing examples any acid stable wetting agent may be used instead of the Aerosol OS, the concentration preferably being within the range of 0.5 to 10% by Weight .of the total addition agent. Other alkalis, such as potassium hydroxide, may also be employed in place of the caustic soda.

With the pickling composition described in Example I the optimum results are obtained by using 1 to 3 parts of said composition per thousand parts by weight of a pickling solution containing either sulfuric acid or hydrochloric acid as the pickling acid.

The pickling temperatures are preferably within the range of 120 F. to 200 F. in sulfuric acid pickling baths and within the rangeoffiil" F. to

120 F. in hydrochloric acid pickling baths.

The thiosulfate or other sulfur liberating compound tends to prevent the formation of alpha and gamma iron oxide and the sulfur which is liberated to some extent also acts as a depolariz- The quantity of sodium thiosulfate or chemically equivalent amount of a sulfur liberating compound'is subject to variation but is preferably within the range of 1 to '8 parts thiocyanate and a compound capable of liberating elemental colloidal sulfur, the quantity of said last named compound being effective to liberate colloidal sulfur in a sufficiently small amount to remain dispersed in colloidal form.

3. A process of conditioning ferrous metal surfaces which comprises immersing the ferrous metal surface to be conditioned in a hydrochloric acid pickling bath containing a water soluble ionizable thiocyanate and a compound capable of liberating elemental colloidal sulfur, the quantity of said last named compound being effective to liberate colloidal sulfur in a sufficiently small amount to remain dispersed in colloidal form.

4. A process of conditioning ferrous metal surfaces which comprises immersing the ferrous metal surface to be conditioned in an acid pickling bath containing sodium thiocyanate and sodium thiosulfate, the quantity of said sodium thiosulfate being effective to liberate colloidal sulfur in sufficiently small amount to remain disof sodium thiosulfate per 700 parts of 7% 5111- furic acid or about 1 to 8 parts colloidal reactivev sulfur in 5000 parts of sulfuric acid. The sodium thiocyanate or another equivalent water soluble ionizable thiocyanate in some unexplained manner makes it possible to produce a very fine grained etch and provides an anti-burn effect.

The quantity of sodium thiocyanate or chemically equivalent amount of another water soluble ionizable thiocyanate is subject to variation but is preferably 3 to 1.0 times the amount of the sodium thiosulfate or other sulfur liberating compound on a chemical equivalent basis.

The addition agent employed in the practice of the invention acts to unify the electrostatic charge over ferrous metal surfaces and remove hydrogen polarization films from cathodic areas. It also serves to prevent the oxidation of aqueous solutions of iron salts remaining on the surfaces of metals which have been immersed in sulfuric or hydrochloric acid pickling solutions. The result is a uniform'micro-etch without excessive acid attack on anodic areas or crystal boundaries persed in colloidal form.

5. A process of conditioning ferrous metal surfaces which comprises immersing the ferrous I 6. A process of conditioning ferrous metal surfaces which comprises immersing the ferrous metal surface to be conditioned in a hydrochloric acid pickling bath containing sodium thiocyanate and sodium thiosulfate, the quantity of said sodium thiosulfate being effective to liberate colloidal sulfur in sufficiently small amount to remain dispersed in colloidal form.

7. An acid pickling bath containing a water soluble ionizable thiocyanate and a compound capable of liberating elemental colloidal sulfur,

' the quantity of said last named compound. being and with substantially no burning ordiscoloration.

can be operated with higher iron concentrations than is possible in ordinary acid pickling baths. Hence, the acid pickling baths prepared in accordance with the present'invention can be used over a longer period of time. The net result is an increase in production capacity and an overall saving in cost. 7

The invention is hereby claimed as follows:

1. A process of conditioning ferrous metal surfaces which comprises immersing the ferrous metal surface to be conditioned in an acid pickling bath containing a water soluble ionizable thiocyanate and a compound capable of liberating ele- Acid pickling baths containing as addition agents the compositions of the present invention metal surface to be conditioned in a sulfuric acid 7 pickling bath containing a water soluble ionizable sufficient to liberate 1 to 8 parts of colloidal sulfur in 5000 parts of acid and the quantity of thiocyanate calculated as sodium thiocyanate being 3 to 10 times the Weight of said sulfur liberating compound calculated as sodium thiosulfate.

8. A sulfuric acid pickling bath containing a water soluble ionizable thiocyanate and 'a compound capable of liberating elemental colloidal sulfur, the quantity of said last named compound being sufficient to liberate 1 to 8 parts of colloidal sulfur in 5000 parts of acid and the quantity of thiocyanate calculated as sodium thiocyanate being 3 to 10 times the weight of said sulfur liberating compound calculated as sodium thiosulfate.

9. A hydrochloric acid pickling bath containing a water soluble ionizable thiocyanate and a dium thiosulfate. V V

10. An acid pickling bath containing'sodium thiocyanate and sodium thiosulfate, the quantity of sodium thiosulfate being suihcient to liberate 1 to 8 parts of colloidal sulfur in 5000 parts of acid and the amount of the sodium, thiocyanate being 3 to 10 times the weight of the sodium lthiosulfate.

11. A'sulfuric acid pickling bath containing sodium thiocyanate and sodium thiosulfate, the

quantity of sodium thiosulfate being sufficient to liberate 1 to 8 parts of colloidal sulfur in 5000 parts of sulfuric acid and the quantity of sodium thiocyanate being 3 to 10 times the weight of the sodium thiosulfate.

12. A hydrochloric acid pickling bath containing sodium thiocyanate and sodium thiosulfate, the quantity of sodium thiosulfate being sufficient to liberate 1 to 8 parts of colloidal sulfur in 5000 parts of acid and the quantity of sodium thiocyanate being 3 to 10 times the weight of the sodium thiosulfate.

13. An addition agent for acid pickling baths consisting essentially of a water soluble ionizable thiocyanate and a compound capable of liberating elemental colloidal sulfur, the quantity of said last named compound being sufficient to liberate 1 to 8 parts of colloidal sulfur in 5000 parts of sulfuric acid and the quantit of said thiocyanate being 3 to 10 times the weight of said sulfur liberating compound, calculated on the basis of sodium thiosulfate.

14. An addition agent for acid pickling baths consisting essentially of sodium thiocyanate and sodium thiosulfate, the quantity of sodium thiosulfate being suificient to liberate 1 to 8 parts of colloidal sulfur in 5000 parts of sulfuric acid and the quantity of sodium thiocyanate being 3 to 10 times the weight of the sodium thiosulfate.

References Cited. in the file of this patent UNITED STATES PATENTS Number Name Date 1,796,839 Gravell et al Mar. 17, 1931 2,249,383 iHilty July 15, 1941 OTHER REFERENCES Modern Inorganic Chemistry, Mellor, 1939, pub. Longmans Green, p. 475. 

1. A PROCESS OF CONDITIONING FERROUS METAL SURFACES WHICH COMPRISES IMMERSING THE FERROUS METAL SURFACE TO BE CONDITIONED IN AN ACID PICKLING BATH CONTAINING A WATER SOLUBLE IONIZABLE THIOCYANATE AND A COMPOUND CAPABLE OF LIBERATING ELEMENTAL COLLOIDAL SULFUR, THE QUANTITY OF SAID LAST NAMED COMPOUND BEING EFFECTIVE TO LIBERATE COLLOIDAL SULFUR IN A SUFFICIENTLY SMALL AMOUNT TO REMAIN DISPERSED IN COLLOIDAL FORM. 